error C2440: '=' : cannot convert from 'void *' to 'mat **'怎么回事阿

typedef struct

{

int ct_levels; /* number of pyramid decomposition levels */

int wt_levels; /* number of wavelet decomposition levels */

ivec dfb_levels; /* number of directional decomposition levels */

mat low; /* low-frequency band */

mat **high; /* high-frequency bands [level][orientation] */

mat *dwt; /* wavelet subband decomposition of 'low' */

vec H0; /* pyramid analysis filter */

vec G0; /* pyramid synthesis filter */

} contourlet_t;



上面好好地 ct->high=calloc(ct_levels, sizeof(mat *)); 这句话报错了 搞不懂为什么 求大神指教！！！！！！